Dairy manure waste fiber to energy process

ABSTRACT

A process for converting waste fibers to solid fuel is provided, including providing a supply of animal waste including the waste fibers in a predetermined quantity; washing the supply of animal waste for a predetermined washing period; dewatering the supply of animal waste by separating water from the waste fibers for a predetermined dewatering period; shedding the waste fibers for separating liquids from solids; compressing the dewatered and shed waste fibers to generate a plurality of briquettes; torrefying at least one of the plurality of briquettes in a torrefaction reactor using a heat source at a predetermined torrefying temperature for a predetermined torrefying period; removing the at least one of the plurality of briquettes from the reactor; and cooling the torrefaction reactor to reach a predetermined cooling temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.15/650,498, filed on Jul. 14, 2017, which is a divisional of U.S.application Ser. No. 14/195,313, filed on Mar. 3, 2014, which claimspriority to a U.S. provisional patent application Ser. No. 61/773,899filed on Mar. 7, 2013 under 35 U.S.C. § 119(e), all of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention is broadly concerned with fuel products formedfrom dairy livestock waste and processes for making and using the fuelproducts. More particularly, the products are formed by cleaning,dewatering, compressing and torrefying dairy livestock waste or manurefiber into solid fuel derived directly from dairy cow waste.

BACKGROUND

There is a tremendous amount of dairy manure waste generated by dairyfarms each year that must be managed. However, there are limited optionsfor disposing of this material, specifically manure coming from dairyConcentrated Animal Feeding Operations (CAFO's). Due to the high densityof cows in such facilities, an extremely large quantity of manure isproduced daily in these facilities, resulting in often strong smells andcontinual odors that are objectionable to many people living near thefacilities. Currently, the waste is usually stored in lagoons due to therelatively high percentage of water in the waste. However, lagoons andother current methods do not eliminate odor problems from dairy farmingoperations. Additionally, current disposal/storage methods, along withland farming, in many cases, run the risk of contaminating the air,land, and water in and around these CAFO's.

At the same time, in the global economy, increasing quantities of fossilfuels are utilized each year for electricity production, heating, steamgeneration, transportation and other needs. There are continual effortsby various environmentally-minded groups to encourage the decreasedconsumption of fossil fuels to preserve the limited quantity of thefuels as well as to decrease the quantity of pollutants produced byburning fossil fuels. While these efforts have had some success, thereis always the need for additional processes and products which utilizeenergy sources other than fossil fuels.

There is a need for products and processes which can utilize dairywastes for producing energy such as heat and power.

SUMMARY

The above-listed need is met by the present process, which features theuse of dairy cow waste manure fiber to form a fuel product. In thepresent process, the manure fiber is washed, dewatered, and compressed,and then undergoes thermal torrefaction. Optionally, the presentprocessed waste material can be recompressed to yield high quantities ofenergy without emitting large quantities of pollutants. Torrefaction isdefined as a thermochemical decomposition of biomass at an elevatedtemperature, without the presence of oxygen. The dewatering,compression, and torrefaction steps produce a solid fuel product, whichis easier to transport and store than waste manure fiber biomass. Insome cases, the processed waste material is ground or pulverized foreasier handling and/or transport.

More specifically, the present invention provides a process forconverting dairy manure waste fibers to solid fuel. The present processincludes providing a supply of animal waste, dewatering the waste, whichincludes waste fibers, compressing the dewatered waste to formbriquettes, and torrefying the briquettes. Prior to the dewatering step,the process further includes washing the dairy manure waste, includingthe waste fibers. During the torrefying step, the process furtherincludes adding cellulous particles to the compressed waste to absorbby-product oils and tar from the fibers. Example cellulous particlesinclude sawdust, absorbent rice hulls, and peanut shells. The torrefyingstep takes place at a temperature up to 700 degrees Fahrenheit, andlasts up to thirty minutes. The compressed briquettes are approximately3.5″ by 2.5″ by 6.0″.

After the torrefying step, the process further includes cooling thebriquettes to below 100 degrees Fahrenheit. The present process furtherincludes recompressing the torrefyed briquettes after the torrefyingstep. The present process further includes pulverizing the torrefyedbriquettes after the torrefying step.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic flow chart depicting the present process.

DETAILED DESCRIPTION

Referring to FIG. 1, the present dairy manure waste fiber to energyprocess system is generally designated 10, and is designed forconverting dairy manure waste fibers to solid fuel. An agitation troughor pit 12 is supplied with a predetermined quantity of fiber 14, such ascow manure waste, including waste fibers. The fibers are the undigestedelements of the cow's diet. The waste fibers 14 are preferably andoptionally washed with a supply of clean recycled water 16 to remove asmuch elemental contamination from the dairy manure fiber to reduceinterference from side effects which may occur upon combustion. Theprincipal elemental contaminant is potassium. It is excreted in thecows' urine and is mixed with cow manure. The side effects of too muchpotassium include that it has a low elemental melting point and cancause problems in furnace and boiler operations when it is present inhigh levels upon the combustion of solid fuel. Some fossil coals alsohave this problem. Washing, in simple terms, cleans the urine, as wellas dirt and soil from the fiber. A water recirculation pump 18 ispreferably provided in or associated with the trough 12 for providingagitation. Any properly sized, commercially available pump is consideredsuitable. In a preferred embodiment, the fiber washing step will take5-10 minutes, depending on the amount of elemental surface contaminationon the fiber.

The fibers 14 are next dewatered by being pumped through piping 20sufficient to carry the weight and amounts of the fiber into adewatering device 22 adequate to handle the weight and volume of manurefiber on a continuous basis to separate the water from the fiber. In apreferred embodiment, the dewatering device 22 is a centrifuge and thisstep can take 5 to 10 minutes, depending on the density of the fiber inthe piping 20. It is also contemplated that other suitable dewateringdevices are employed at this point in the process, including but notlimited to dewatering screens, presses and the like. Preferably, thedewatering device is operated at a velocity that will reduce the fibers14 to approximately 70% moisture by weight.

The dewatering device 22 is then slowed to allow the fiber 14 to be shedfrom the centrifuge by means of a manure drum roller system 24. A drumroller is a piece of agricultural equipment used in the liquid-solidsseparation process. It allows for the manure to roll, at less velocitythan a centrifuge, so that it stays loose and does not compact so as tomake it easier to handle as it moves on to a screw press device as anear end stage of water removal. The manure drum roller system 24 isused to continue removing water from the fiber, and allows air contactwith the fiber where it can “cake.” The fiber 14 is released from theroller system 24 for the purpose of entering piping 26 sufficient tocarry the weight and volume of fiber to be received by a dairy manurefiber screw press 28.

The screw press 28 should be sufficient to handle the volume and weightof the fiber, is operated continuously, and is preferably automated.After passing through the press 28, the fiber 14 will then beapproximately 60-65% moisture content by weight in a preferredembodiment. The fiber 14 is moved by the screw press 28 via a conveyor30 to a dry storage area 32, where it can be collected in any amountsnecessary to prepare it for further drying via commercially availablerotary or drum drying. Those familiar with the art are aware of thesefurther drying devices. These further drying procedures, in a preferredembodiment, will reduce the fiber moisture content to 10 to 12% (orlower). Those familiar with the art should also understand theoperational use of these devices as they are commercially available fromvarious manufacturers.

The fiber 14 is then compressed with a cold briquetting device 34. In apreferred embodiment, the cold briquetting device 34 compresses thefiber at up to 50 English tons of force or greater. Those individualsfamiliar with the art should know that one can substitute any equivalentbriquetting device for equivalent size and strength compression. In thepreferred embodiment, the briquettes 36 formed by the cold briquettingdevice 34 are 3.5″ by 2.5″ by 6.0″ (height by width by length). Othersizes are contemplated depending on the application. Forming thebriquettes 36 with the cold briquetting device 34 allows for ease ofmovement and handling of the fiber 14 to move it to a torrefactionreactor, generally designated 38.

Before placing the briquettes 36 in the reactor 38, cellulous particlesare preferably first sprinkled at the bottom of the reactor 38 to absorbby-product oils and tar from the fiber torrefaction step. In a preferredembodiment, clean sawdust works well, but absorbent rice hulls or peanutshells can also be used in place of the clean sawdust lining the bottomof the reactor 38.

In a preferred embodiment, the reactor 38 is preheated to 350 degreesFahrenheit to help speed the torrefaction process. The reactor 38,depending on how it is heated, should have an internal thermometer 40for measuring the internal temperature, as well as an externalthermometer 42. In the present process, in certain embodiments twodifferent heat sources were used on two different reactors. In oneembodiment, a wood fired source of heat was used on a double walledreactor. The external thermometer 42 is employed to gauge firedtemperature around the reactor. On the alternative propane heated model,the external thermometer 42 is retained due to the speed at reachingtemperatures first in the lower part of the reactor. Both reactor typeshave the internal thermometer 40 installed on a sealed lid 44 of thereactor 38. A vacuum seal (not shown) is used via a vacuum pump (notshown) to prevent combustion of the reactor 38 while the fiberbriquettes 36 are in the reactor. The sealed lid 44 at an opening of thereactor 38 is necessary for reducing the entry of outside oxygen intothe reactor 38. It is contemplated that the seal is pressurized, butoptionally may be non-pressurized.

The external heat source, generally designated 46, is configured forgenerating heat applied to the reactor 38 for the torrefaction step, andcan be from any commercially available apparatus, such as a propane gasburner 48. The reactor 38 is preferably disposed above the gas burner48, which is supplied with fuel by a propane tank 50 by a propane feedline 52. Other heating sources may be used in place of propane, such aswood, coal, or charcoal.

The torrefaction or torrefying step within the reactor 38, in apreferred embodiment, lasts up to 30 minutes depending on the amount offiber briquettes 36 in the reactor 38. Also in a preferred embodiment,the torrefaction is carried out in the approximate range of 600 to 700degrees Fahrenheit. The torrefaction step is complete when an evidenceof gaseous discharge (via internal vapor pressures) or bio-oil residueis observed around the reactor lid 44.

Next, the reactor 38 is removed from the external heat source 46, andallowed to cool down. While the reactor 38 is cooling down, the lid 44should remain closed to prevent the exposure of the briquettes 36 tofresh oxygen through the ambient air. In a preferred embodiment, theinternal temperature of the reactor should cool to below 100 degreesFahrenheit (below 80 degrees Fahrenheit is preferred) before opening thereactor 38. Prior to removal from the reactor 38, the briquettes 36should appear well formed and darkened due to the torrefaction process.

After the briquettes 36 are removed from the reactor 38, the briquettescan be recompressed to prepare them for water solubility/hydroscopictesting effects. This recompression step would be necessary for opencontainer shipping, as is the case for rail shipping for fossil coal.The briquettes 36 are also optionally comminuted, ground or pulverizedfor packaging and shipping. Those familiar in the art of this processshould know that it is possible to compress sooner in the overallprocess dependent on the feedstock used, residence time in the reactor38, and packaging and shipping chosen.

While a particular embodiment of the process has been described herein,it will be appreciated by those skilled in the art that changes andmodifications may be made thereto without departing from the inventionin its broader aspects and as set forth in the following claims.

The invention claimed is:
 1. A system for converting waste fibers tosolid fuel, the system comprising: a centrifuge configured to receive amixture of animal waste and water and provide dewatered fibers; a drumroller configured to receive the dewatered fibers from the centrifugeand to provide shredded fibers; a screw press connected downstream ofthe drum roller, and configured to receive the shredded fibers and toprovide a reduced water content shredded fibers; a briquetting devicedownstream of the screw press, and configured to provide at least onecompressed fiber briquette; and a torrefaction reactor configured toreceive the at least one compressed fiber briquette and provide at leastone solid fuel briquette; and wherein the torrefaction reactor comprisesan external heat source configured to heat the at least one compressedfiber briquette indirectly.
 2. The system of claim 1, furthercomprising: a dry storage area between the screw press and thebriquetting device; and a conveyer disposed upstream of the dry storagearea and configured to receive reduced water content shredded fibers. 3.The system of claim 2, wherein the dry storage area comprises a dryer.4. The system of claim 1, further comprising: a pump configured toprovide the mixture of animal waste and water, via piping, to thecentrifuge.
 5. A process for converting waste fibers to solid fuel, saidprocess comprising: providing a supply of animal waste including thewaste fibers; washing the supply of animal waste for a washing periodsufficient to remove at least one of urine, dirt, and soil from theanimal waste to provide a washed animal waste; removing water from saidwashed animal waste to provide waste fiber comprising less than 70%water, by weight; shredding said waste fibers; compressing the wastefibers after said shredding to generate a plurality of briquettes;torrefying at least one of the plurality of briquettes in a torrefactionreactor using a heat source which is an external heat source in theabsence of oxygen at a temperature for a time period sufficient toprovide a torrefied briquette, wherein said temperature of saidtorrefying step ranges between 600 and 700 degrees Fahrenheit; and,recovering the torrefied briquette from the reactor.
 6. The process ofclaim 5, further comprising: cooling the torrefaction reactor to atemperature below the temperature during said torrefying step.
 7. Theprocess of claim 6, wherein said temperature of said cooling step isbelow 100 degrees Fahrenheit.
 8. The process of claim 5, wherein saidproviding step is performed first, said washing step is performed aftersaid providing step, said dewatering step is performed after saidwashing step, said compressing step is performed after said dewateringstep, and said torrefying step is performed after said compressing step.9. The process of claim 5, wherein said time period of said torrefyingstep lasts up to thirty minutes.
 10. The process of claim 5, wherein adimension of the briquettes from the plurality of briquettes isapproximately 3.5″ by 2.5″ by 6.0″.
 11. The process of claim 5, furthercomprising: compressing the torrefied briquette after said torrefyingstep.
 12. The process of claim 5, further comprising: pulverizing thetorrefied briquette after said torrefying step.
 13. The process of claim5, further comprising: removing oxygen from the torrefaction reactorprior to torrefying at least one of the plurality of briquettes in thetorrefaction reactor.
 14. The process of claim 5, further comprising:preheating the torrefaction reactor to 350 degrees Fahrenheit beforetorrefying at least one of the plurality of briquettes in thetorrefaction reactor.
 15. The process of claim 5, wherein thetorrefaction reactor includes a lid, and wherein the process includes:sealing the lid to the torrefaction reactor before torrefying at leastone of the plurality of briquettes in the torrefaction reactor.